apic: init apic timer using pit, not precise on qemu

include/apic.h

@@ -17,4 +17,8 @@ uint32_t ioapic_read(void *ioapicaddr, uint32_t reg);
 void ioapic_write(void *ioapicaddr, uint32_t reg, uint32_t value);
 void ioapic_redirect(int gsi, int vector);
 
-void enable_symmetric_io_mode();
+void enable_symmetric_io_mode();
+
+void init_pit_timer_apic(uint32_t reload_value);
+void init_apic_timer();
+void mask_pit_interrupt();

include/isr.h

@@ -1,6 +1,10 @@
 #ifndef ISR_H
 #define ISR_H
 
+#include <stdint.h>
+
+extern uint32_t timer_ticks;
+
 void isr0();
 void isr1();
 void isr2();

src/kernel/apic.c

@@ -125,4 +125,59 @@ void ioapic_redirect(int gsi, int vector) {
 void enable_symmetric_io_mode() {
    outb(0x22, 0x70);  // Select IMCR
    outb(0x23, 0x01);  // Set to Symmetric I/O mode (bypass PIC)
+}
+
+#include "../include/isr.h"
+
+#define APIC_REGISTER_TIMER_DIV 0x3E0
+#define APIC_REGISTER_TIMER_INITCNT 0x380
+#define APIC_REGISTER_LVT_TIMER 0x320
+#define APIC_LVT_INT_MASKED 0x10000
+#define APIC_REGISTER_TIMER_CURRCNT 0x390
+#define APIC_LVT_TIMER_MODE_PERIODIC (1 << 17)
+
+void init_pit_timer_apic(uint32_t reload_value) {
+   int timerFrequency = 1193182 / reload_value;
+ 
+   outb(0x43, 0b00110100);
+ 
+   uint8_t l = (uint8_t)(timerFrequency & 0xFF);
+   uint8_t h = (uint8_t)(timerFrequency >> 8 & 0xFF);
+ 
+   outb(0x40, l);
+   outb(0x40, h);
+}
+
+void init_apic_timer()
+{
+   lapic_write(APIC_REGISTER_TIMER_DIV, 0x3);
+ 
+   // Prepare the PIT to sleep for 10ms (10000µs)
+   init_pit_timer_apic(1000);
+
+   __asm__ __volatile__ ("sti");
+
+   // Set APIC init counter to -1
+   lapic_write(APIC_REGISTER_TIMER_INITCNT, 0xFFFFFFFF);
+
+   uint32_t target_ticks = timer_ticks + 10;//+10ms
+   while(timer_ticks < target_ticks)
+   {}
+
+   // Stop the APIC timer
+   lapic_write(APIC_REGISTER_LVT_TIMER, APIC_LVT_INT_MASKED);
+
+   // Now we know how often the APIC timer has ticked in 10ms
+   uint32_t ticksIn10ms = 0xFFFFFFFF - lapic_read(APIC_REGISTER_TIMER_CURRCNT);
+
+   // Start timer as periodic on IRQ 0, divider 16, with the number of ticks we counted
+   lapic_write(APIC_REGISTER_LVT_TIMER, 32 | APIC_LVT_TIMER_MODE_PERIODIC);
+   lapic_write(APIC_REGISTER_TIMER_DIV, 0x3);
+   lapic_write(APIC_REGISTER_TIMER_INITCNT, ticksIn10ms);
+}
+
+void mask_pit_interrupt() {
+   // Mask PIT interrupt (GSI 0, IRQ 0)
+   ioapic_write(ioapic_ptr, REG_TABLE + 2 * 0, INT_DISABLED | T_IRQ0);
+   ioapic_write(ioapic_ptr, REG_TABLE + 2 * 0 + 1, 0); // Clear destination field
 }

src/kernel/isr.c

@@ -110,8 +110,11 @@ __attribute__((interrupt)) void spurious(struct interrupt_frame *frame)
     lapic_eoi();
 }
 
+uint32_t timer_ticks = 0;
+
 __attribute__((interrupt)) void isr_timer(struct interrupt_frame *frame)
 {
+    timer_ticks++;
     if(lapic_enabled)
     {
         lapic_eoi();

src/kernel/kernel.c

@@ -73,6 +73,9 @@ void kmain(unsigned int magic, unsigned int info)
 		printf("IOAPIC init done\n");
 		ioapic_redirect(2, 32);//timer
 		ioapic_redirect(1, 33);//keyboard
+
+		init_apic_timer();
+		mask_pit_interrupt();
 	}
 
 	printf("done fucking with pages and memory map!\n");
@@ -132,6 +135,11 @@ void kmain(unsigned int magic, unsigned int info)
 
 	while(1)
 	{
+		if(timer_ticks % 1000 == 0)
+		{
+			//printf("a second should have passed!\n");
+		}
+
 /*		if(inportb(0x64) & 0x1)
 		{
 			unsigned char key = inportb(0x60);